The present invention relates to an apparatus for fabricating chipboards or fiber boards of cellulose material, such as wood, straw, reed, cotton stems, paper or the like, by means of a continuously or discontinuously, operating press.
In the fabrication of cellulose fiber boards or cellulose chipboards, the formation of a material mat before carrying out the actual pressing operation and hardening of the boards strands is crucial. In this context, the standards that have to be met by a material spreading station with respect to size accuracy, i.e. width, length and thickness of the mat and distribution of differently sized chips within the mat as well as angular position of the chips with respect to the main surface of the board are high.
These standards are even further heightened through the emergence of continuously operating board presses and the associated considerable material saving (reduced grinding allowance and reduced sawing waste). However, a double belt press has only very limited capability to compensate e.g. significant size variations encountered when chips or fibers are incorrectly spread onto the press.
Spreading stations are known which fabricate the fiber mat or the chip mat mechanically on a continuously advanced spreading band by means of discharge drums (gravity-type spreading process) or through use of blowers (wind-type spreading process). In order to meet the standards, as referred to above, bulky and complex machines have been developed. In all cases, various storage bins are provided which have an outlet opening above the plane of the spreader band for discharge of chips which drop in free fall onto the spreader band on which the chips orient under the influence of gravity substantially parallel to the conveying direction of the band and thus parallel to the main surface of the board being fabricated. This alignment is retained on continuously or discontinuously operating presses in flat press operation because the pressing force is applied perpendicular to the main surface of the pressed strand, with the scattered particles being aligned perpendicular to the pressing force and thus parallel to the main surface. As a consequence, the chipboards exhibit a high bending strength.
In conventional extrusion processes, the chips are pressed by an oscillating plunger through a die passage, with the force applied by the plunger acting in conveying direction. The chips are oriented perpendicular to the piston force and thus perpendicular to the main surface of the pressed strand so that the extruded boards are afforded a high tensile strength in transverse direction but only a slight bending strength.